Conventionally, a seat for a vehicle in which a seat back can be inclined relative to a seat cushion in a desired manner by means of an electrical means has been used.
The Japanese Patent Laid-open Publication 2006-306188, for instance, discloses one example of such a seat for a vehicle.
Such a seat for a vehicle comprises a seat back frame structure a lower end of which is connected to a rear end of a seat cushion frame structure in such a way that the seat back frame structure can be inclined relative to the seat cushion frame structure. The seat back frame structure includes a pair of side frames each of which extends in a vertical direction of the vehicle. A through-hole is provided on a lower end portion of each of the pair of side frames, a connecting rod which extends through each of the through-holes is provided so as to be rotatable about a horizontal direction. An electrical reclining motor which rotates said connecting rod is provided along the one of side surfaces of the one of said pair of side frames. A reclining apparatus is provided on the other of the side surfaces of each of said pair of side frames.
The reclining apparatus comprises an internal teeth gear which includes internal teeth and is fixed to the one of the pair of side frames, an external teeth gear which is concentric to the connecting rod and includes outer teeth whose number of teeth is less than that of the internal teeth, and an external teeth gear which is concentric to the connecting rod so as to mate with the internal teeth gear and is fixed on the seat cushion frame structure, and an eccentric driving means for driving said internal teeth gear in an eccentric manner by being driven by means of the rotation of the connecting rod.
According to the seat for a vehicle including the above structure, the seat back frame structure can be inclined relative to the seat cushion frame structure in a desired manner by rotating the connecting rod about a horizontal direction by driving the electrical reclining motor and using the eccentric driving means of the reclining apparatus to drive the internal teeth gear in an eccentric manner so as to make the external teeth whose number of the teeth is less than that of the internal teeth mate with the internal teeth.
However, in the above seat for a vehicle, a following technical problem arises due to the fact that the electrical reclining motor and the reclining apparatus do not constitute a single unit, but are provided separately from each other.
In a case where the electrical reclining motor is fixedly connected on the one of the pair of side frames of the seat back frame structure, the electrical reclining motor can become inclined due to the fact that the electrical reclining motor is diagonally mounted on a seat back frame structure, or that the seat back frame structure is deformed after such a connection.
In such a case, a stable reclining action becomes difficult, since hammering (foreign sound) is generated between a shaft and the connecting rod, and the shaft or the connecting rod can become worn with time.
In short, it is technically difficult to smoothly adjust the reclining of the seat back by driving the electrical reclining motor.